Recommended way to create an ActionResult with a file extension

Question

I need to create an ActionResult in an ASP.NET MVC application which has a .csv filetype.

I will provide a 'do not call' email list to my marketing partners and i want it to have a .csv extension in the filetype. Then it'll automatically open in Excel.

 http://www.example.com/mailinglist/donotemaillist.csv?password=12334

I have successfully done this as follows, but I want to make sure this is the absolute best and recommended way of doing this.

    [ActionName("DoNotEmailList.csv")]
    public ContentResult DoNotEmailList(string username, string password)
    {
            return new ContentResult()
            {
                Content = Emails.Aggregate((a,b)=>a+Environment.NewLine + b), 
                ContentType = "text/csv"
            };
    }

This Actionmethod will respond to the above link just fine.

I'm just wondering if there is any likelihood of any unexpected conflict of having the file extension like this with any different version of IIS, any kind of ISAPI filter, or anything else I cant think of now.

I need to be 100% sure because I will be providing this to external partners and don't want to have to change my mind later. I really cant see any issues, but maybe theres something obscure - or another more "MVC" like way of doing this.

Heida

Answer 1

I think your Response MUST contain "Content-Disposition" header in this case. Create custom ActionResult like this:

public class MyCsvResult : ActionResult {

    public string Content {
        get;
        set;
    }

    public Encoding ContentEncoding {
        get;
        set;
    }

    public string Name {
        get;
        set;
    }

    public override void ExecuteResult(ControllerContext context) {
        if (context == null) {
            throw new ArgumentNullException("context");
        }

        HttpResponseBase response = context.HttpContext.Response;

        response.ContentType = "text/csv";

        if (ContentEncoding != null) {
            response.ContentEncoding = ContentEncoding;
        }

        var fileName = "file.csv";

        if(!String.IsNullOrEmpty(Name)) {
            fileName = Name.Contains('.') ? Name : Name + ".csv";
        }

        response.AddHeader("Content-Disposition",
            String.Format("attachment; filename={0}", fileName));

        if (Content != null) {
            response.Write(Content);
        }
    }
}

And use it in your Action instead of ContentResult:

return new MyCsvResult {
    Content = Emails.Aggregate((a,b) => a + Environment.NewLine + b)
    /* Optional
     * , ContentEncoding = ""
     * , Name = "DoNotEmailList.csv"
     */
};

Champagne

thanks! but can you clarify what you mean by MUST ? what i had does appear to work - although this way is much more preferable – Heida

If your Action returns ".csv" file then your clients want to "open" it or "save" it - so you must provide "Content-Disposition" header (although it is optional, see ietf.org/rfc/rfc2183.txt). Without this header the process of opening your file may differ in various browsers/OSes/machines – Champagne

Is there an error in the code? Shouldn't Name be a string instead of encoding? Also the compiler is telling me that ActionResult doesn't have a Response property – Norman

Thanks, AD - Name property fixed. ActionResult does not have Response property, but context.HttpContext has one. – Champagne

I've found the bug (Response.Headers.Add ...) - fixed (should be response.Headers.Add ...) - thanks again AD. – Champagne

MVC2 ASP.NET 4.0: Use response.AppendHeader instead of response.Headers.Add. – Himeji

Got an error when running this code (MVC2, ASP.Net 3.5): "This operation requires IIS integrated pipeline mode". Looks like need to change response.Headers.Add to response.AddHeader - platinumbay.com/blogs/dotneticated/archive/2010/10/07/… – Maineetloire

Thanks, useful improvement over the standard ContentResult – Paolapaolina

Answer 2

I used the FileContentResult action to also do something similar.

public FileContentResult DoNotEmailList(string username, string password)
{
        string csv = Emails.Aggregate((a,b)=>a+Environment.NewLine + b);
        byte[] csvBytes = ASCIIEncoding.ASCII.GetBytes( csv );
        return File(csvBytes, "text/csv", "DoNotEmailList.csv");
}

It will add the content-disposition header for you.

Cobden

Makes much more sense than writing a class to do something that's already built in! Cheers! – Consensus

Thanks for a simple clean answer that is easy to implement in another situation – Disaster

Answer 3

This is how I'm doing something similar. I'm treating it as a download:

var disposition = String.Format(
  "attachment;filename=\"{0}.csv\"", this.Model.Name);
Response.AddHeader("content-disposition", disposition);

This should show up in the browser as a file download with the given filename.

I can't think of a reason why yours wouldn't work, though.

Marvamarve

Answer 4

The answer you accepted is good enough, but it keeps the content of the output in memory as it outputs it. What if the file it generates is rather large? For example, when you dump a contents of the SQL table. Your application could run out of memory. What you do want in this case is to use FileStreamResult. One way to feed the data into the stream could be using pipe, as I described here

Tarsia